What is the purpose and procedure of an echo with bubble study (echocardiogram with bubble contrast agent)?

Echo with Bubble Study: Purpose and Procedure

An echo with bubble study (contrast echocardiography) is primarily used to detect intracardiac or intrapulmonary shunts, particularly patent foramen ovale (PFO) and pulmonary arteriovenous malformations (PAVMs), by injecting agitated saline containing microbubbles intravenously while performing echocardiography. 1

Purpose of Bubble Studies

• Bubble studies are essential for detecting right-to-left shunts, which is considered a standard requirement for echocardiography training 2
• They help identify potential causes of cryptogenic stroke, where PFO may lead to paradoxical embolism 1
• These studies are crucial for evaluating patients with suspected congenital heart defects by verifying the presence of shunts 1
• Bubble studies assist in diagnosing pulmonary arteriovenous malformations, particularly in patients with hereditary hemorrhagic telangiectasia, with transthoracic echocardiography with contrast showing 98-99% sensitivity for detecting PAVMs 1
• They help identify intracardiac shunts that may contribute to or complicate pulmonary hypertension 1

Procedure of Bubble Study

Technical Aspects

• The procedure involves injecting agitated saline containing highly reflective gas-filled microbubbles intravenously while performing echocardiography 3
• Microbubbles in the solution typically range from 1 to 15 microns in diameter, with mean bubble diameters less than 6 microns 4
• Bubble studies can be performed during both transthoracic (TTE) and transesophageal (TEE) echocardiography 1
• TEE provides higher sensitivity (51% vs. 32%) for detecting shunts compared to TTE 1

Contrast Agent Preparation

• Sonication is a reliable and reproducible technique for preparing standardized echo contrast agent solutions containing uniformly small microbubbles 4
• Commercial ultrasound contrast agents (microbubbles) are also available and recommended during stress echocardiography to improve diagnostic accuracy 2
• The concentration of bubbles is directly proportional to echo-reflective properties, with solutions showing significant ultrasound reflective properties even at concentrations below 1500 bubbles/ml 4

Clinical Applications

Stroke Evaluation

• Bubble studies are particularly valuable in evaluating cryptogenic stroke patients to identify PFO as a potential cause 1
• They help identify patients who might benefit from PFO closure to prevent recurrent stroke 1
• However, bubble studies are frequently performed in patients with readily identifiable causes of stroke, where any PFO detected is likely incidental 5
• A study found that only 31% of patients with detected PFO had a subsequent change in management 5

Cardiac Assessment

• During stress echocardiography, when two or more contiguous myocardial segments are not visualized, intravenous ultrasound contrast agents are recommended to improve diagnostic accuracy 2
• Myocardial perfusion using contrast agents during stress echocardiography is recommended to improve diagnostic accuracy and refine risk stratification beyond wall motion 2
• Bubble studies complement standard echocardiography in evaluating complex congenital heart defects 1

Safety Considerations

• The procedure is generally safe with a very low complication rate (0.1% risk of TIA in one study), but this warrants informed consent 5
• Level III training in contrast echocardiography should include instruction on the chemical composition and physical properties of ultrasound enhancing agents, advanced ultrasound equipment settings, safety issues, and protocols 2

Optimizing Clinical Utility

• A noninvasive strategy combining carotid intima-media thickness assessment, plaque screen, and transthoracic echocardiography bubble study can identify patients in whom further invasive evaluation with TEE will be of low diagnostic yield 6
• Recent studies suggest that bubble studies are often performed in non-cryptogenic stroke patients where findings rarely change management, indicating a need for more selective use 7

Note: The bubble study is a valuable diagnostic tool that should be used appropriately based on clinical indications to maximize its utility while minimizing unnecessary testing.